You can get very nice luxury bus trips from almost any point to any point in Argentina. Many lines have essentially flat bed seats that fold out and allow you to sleep quite well, and you wake up in the next city. I particularly liked the company Via Bariloche, and traveled all around the country with them. Saves the cost of a night in a hotel as well. I also had nice service from the Andesmar bus company, though not a fully flat bed, more like a first class airline seat.
Nice benefit is that you get to see more of the country as you travel.